This invention relates generally to the field of location-position systems, methods and apparatuses and, in particular embodiments, to relay assisted location-position systems, methods and apparatuses which employ the use of Radio Frequency (RF) tags and data relays.
Location position (LP) systems ascertain positions of particular objects and/or track the locations of objects. Historically, location position systems have been quite diverse. Some location position (LP) systems and processes have typically employed sensor devices, such as motion sensors, heat sensors, or the like, for detecting the presence of an object or personnel to be located or tracked. Other LP systems have employed labels or tag elements, such as, for example, bar codes, RF labels, short-range RF tags, long-range RF tags, and the Global Positioning System (GPS) which provide a signal that has location information or is indicative of location by virtue of its transmission.
A simplistic example of a military application utilizing a rudimentary position system is the proximity sensor used in anti-personnel landmines. An anti-personnel mine is basically a proximity sensor coupled to an explosive charge. An anti-personnel landmine is one that detects the presence of a target, for example an enemy soldier, and in response, initiates an explosive charge within the proximity of the detected enemy. Such anti-personnel landmines typically detect whether a target is present or absent from a designated area (i.e. in a local position), but do not track or ascertain actual locations.
Anti-personnel land mines have several disadvantages as a military position detection system. A first disadvantage is that the activation of one anti-personnel landmine provides a warning to any enemy of the possible presence of other landmines. A first anti-personnel landmine detonation may provide an element of surprise, but once a first anti-personnel landmine has detonated, any other enemy target within the area will be alerted to the possible presence of other anti-personnel landmines.
A second drawback of typical anti-personnel landmines is that it does not discriminate between friend and foe. Friendly forces wandering into an anti-personnel landmine area may be destroyed by such mines. Such anti-personnel landmines are also a threat to friendly forces, during deployment. For example, a mine may be accidentally activated or may be activated by the initiation of hostilities before the placement of the mine can be complete. Typical anti-personnel landmines also are nondiscriminatory. That is, they may be detonated by nonmilitary personnel in the area, or remain deployed and active well after hostilities cease.
In some commercial applications, a LP system comprises machine readable labels or tags have been placed on products or items for inventory control and tracking. In other commercial applications, RF transmitting tags have been affixed to, for example, personnel, vehicles, or other objects to monitor or track the position of such vehicles.
A variety of commercial type location-position systems are available from various manufacturers. One example of commercial (LP) systems is the Tiris(trademark) system from Texas Instruments. A typical Tiris(trademark) system could illustratively comprise a Tiris(trademark) transponder and a RFID (radio frequency identification tag) that can be attached or embedded within objects. A Tiris(trademark) unit sends a radio frequency signal to the tag and the tag broadcasts its stored data back to the Tiris(trademark) unit. The data broadcast back to the Tiris(trademark) unit includes a unique 20-digit code that identifies the RFID tag to the Tiris(trademark) unit. Such a system provides an identification of an RF tag in close proximity to a Tiris(trademark) reader. It, however, provides no location information. Although the Tiris(trademark) system can identify an RF tag, it cannot track it.
Other commercial systems provide tracking capability. One such commercial system that provides tracking capability is provided by PinPoint Corporation of Billerica, Mass. PinPoint provides a product called a 3D-iD(trademark) location position system. The PinPoint system comprises three basic building blocks: RF tags, cell controllers and software. The 3D-iD(trademark) tags can be attached the item desired to be tracked. The tag receives 2.4 ghz spreads spectrum signals from the 3D-iD(trademark) system antennas and responds with a 5.8 ghz signal which includes data uniquely identifying the tag. Tags can be read at ranges up to 200 feet and hundreds of tags can be read by a single cell controller.
The 3D-iD(trademark) cell controllers coordinate exchange of data between antennas and the tags. The cell controllers communicate with the tags via a 2.4 GHz radio signal. The controllers then receive a re-transmitted signal and calculate the time delay between the originally transmitted 2.5 GHz signal and the return 5.8 GHz signal. By receiving the return signal from the tags with several antennas and noting the difference in the time delay the exact identity and location of the tags can be determined.
The PinPoint system also comprises viewpoint software which allows a user to display the information gathered by the PinPoint system. The PinPoint system can offer both identity and location information in range.
While various military and commercial location or tracking systems have been developed, many systems tend to require relatively large and/or expensive tags disposed on the objects or personnel to be located or tracked. Other systems employ relatively unsophisticated detecting or sensing devices such as proximity sensors that do not sufficiently discriminate between intended targets and non-target objects or personnel. Proximity sensors can detect only presence but cannot tell if friend or foe has been detected. As such, the practical application of such systems has been limited.
Military systems have also employed methods such as automatic target recognition (ATR). Automatic target recognition employs signal processing methods which attempt to recognize sound signatures of targets. By processing the sound emitted by various targets, frequency and amplitude relationships can be identified that can be used to distinguish various targets. In addition, by applying multiple sensors and directional principals a target can be located.
While automatic target recognition can be effective, environmental factors such as wind, rain, and noise can interfere with ATR and render it inaccurate.
To address limitations in the prior art described above, and to address other limitations that will become apparent upon reading and understanding the present specification, an RF tag and tracking system, comprises a plurality of tags (preferably, low-power, radio frequency (RF) identification tags), and a base station and intermediate tracking relays is disclosed. In certain embodiments of the present invention, intermediate relays provide single or multi level links between low-powered RF tags and the tracking base station.
According to one embodiment of the invention, each tag is provided with processing circuitry for determining the location position of the tag. According to another exemplary embodiment, position determining computations or functions are instead performed in intermediate relay nodes, which serve as intermediate units between the tags and the positioning base station. In yet a further exemplary embodiment, position determination functions are centralized in a base station, thereby relieving the tags and the intermediate relays of the burden of location position determination.
According to further embodiments of the present invention, tags are automatically activated by a trigger mechanism, for example, upon deployment of the tags. Such a trigger mechanism may also load information corresponding to an initial position into tags, for example, from a GPS signal produced within a deploying mechanism. The tag position can then be tracked by an internal navigation system within the tag.
Further embodiments of a system in accordance with the principles of the invention may include additional aspects and alternate implementations. One such aspect relates to the employment of various networking technologies to extend the tracking range of the tags, as well as providing for robust communications. For example, to address a situation in which a number of relays are destroyed or otherwise not functioning. Relays provide multiple paths for conveying information from the tags to a base station.
Embodiments of the present invention include features that simplify the transmit control. Because the tags transmit asynchronously they do not need a receive function to coordinate transmission between tags. Without a receive function, RF transmissions from the tags cannot be disrupted by an interruption of synchronizing information, because the tags do not accept synchronizing information. In addition, dispensing with the need to synchronize transmissions simplifies control within the tags. The tags transmit at pseudo-random periods instead of continuously. Pseudo-random transmit periods may be determined by pseudo-random number generators within each tag. The pseudo-random number generators may have a built-in seed number, for example, implanted during manufacture, to generate pseudo-random numbers or may generate pseudo-random numbers using pre-assigned tag identification numbers, serial numbers, or the like. In addition to providing communications with low probability of exploitation (LPE) by transmitting at pseudo-random times thereby making it more difficult for an enemy to lock on to transmissions, the tags are able to conserve energy by not transmitting in a continuous mode. Because the tags transmit sporadically, power can be conserved by power cycling parts of the circuitry within the tag when they are not being used. Additionally, the sporadic transmission allows more tag transmissions with reduced transmission collision at the relays or base stations. Additional tag transmissions can be accommodated by increasing the mean time between transmissions from the tags. The mean time between transmissions can be increased by changing the software which generates the pseudo random transmit periods.
Tags can also be tailored for specific applications, for example, tag transmissions can incorporate information in addition to an identifier. For example, in warehousing applications the tag may incorporate a list of items stored within a container. A tag then would not only give the position of the container, but also a list of its contents.
These and other advantages and features of embodiments of the invention will be apparent to those skilled in the art from the following detailed description of preferred embodiments, when read with the drawings and appended claims.